“I cannot imagine topping that experience," Radin told PEOPLE exclusively of his performance for DeGeneres, 50, and de Rossi, 35. "I've never played a wedding before, and I probably won't again until it's my own.”

For his performance, Radin – who was hand-picked by DeGeneres as a surprise for de Rossi – sang acoustic renditions of several new tracks, including the ballad "They Bring Me To You."

But Radin isn’t the only one to share his happiness for the newlyweds: Congratulations have started flooding in. "I wish her all the best, all the happiness, all the joy that comes with that certificate in hand," Katherine Heigl, a self-proclaimed fan of DeGeneres, said upon hearing the news.

America Fererra added that she has no advice for the couple, only well-wishes. "I'm just so happy that they get to love each other in such an official way."

Grey's Anatomy star T.R. Knight also sent his congrats along with his relief that same-sex marriage is now legal in California. "I happy that they’re happy," said Knight. "I’m happy that they’re allowed to get married."

For more on Ellen and Portia's wedding and exclusive personal photos, pick up the new issue of PEOPLE on newsstands Friday